The Pacific oyster (Crassostrea gigas) is an important aquaculture species world-wide. Due to its wide environmental tolerance and high growth rate, it has also become a successful invader in many areas, leading to major ecosystem changes. Low water temperatures were previously believed to restrict the establishment of Pacific oysters in Scandinavia. However, recent surveys reveal that the Pacific oyster is now established in many areas in Scandinavia. We present data on the current distribution, abundance and age-structure in Denmark, Sweden and Norway. The biomass of oysters in the Danish Wadden Sea increased from 1,056 to 6,264 tonnes between 2005 and 2007. Massive settlements were observed along the Swedish west coast in 2007, with densities [400 oysters per m -2 . In Norway, populations are established on the southern coast, and specimens have been found as far north as 60°N. The potential impacts and probable causes of this recent large-scale establishment are discussed.

Barnacles are sessile macro-invertebrates, found along rocky shores in coastal areas worldwide. The euryhaline bay barnacle Balanus improvisus (Darwin, 1854) (= Amphibalanus improvisus) can tolerate a wide range of salinities, but the molecular mechanisms underlying the osmoregulatory capacity of this truly brackish species are not well understood. Aquaporins are pore-forming integral membrane proteins that facilitate transport of water, small solutes and ions through cellular membranes, and that have been shown to be important for osmoregulation in many organisms. The knowledge of the function of aquaporins in crustaceans is, however, limited and nothing is known about them in barnacles. We here present the repertoire of aquaporins from a thecostracan crustacean, the barnacle B. improvisus, based on genome and transcriptome sequencing. Our analyses reveal that B. improvisus contains eight genes for aquaporins. Phylogenetic analysis showed that they represented members of the classical water aquaporins (Aqp1, Aqp2), the aquaglyceroporins (Glp1, Glp2), the unorthodox aquaporin (Aqp12) and the arthropod-specific big brain aquaporin (Bib). Interestingly, we also found two big brain-like proteins (BibL1 and BibL2) constituting a new group of aquaporins not yet described in arthropods. In addition, we found that the two water-specific aquaporins were expressed as C-terminal splice variants. Heterologous expression of some of the aquaporins followed by functional characterization showed that Aqp1 transported water and Glp2 water and glycerol, agreeing with the predictions of substrate specificity based on 3D modeling and phylogeny. To investigate a possible role for the B. improvisus aquaporins in osmoregulation, mRNA expression changes in adult barnacles were analysed after long-term acclimation to different salinities. The most pronounced expression difference was seen for AQP1 with a substantial (>100-fold) decrease in the mantle tissue in low salinity (3 PSU) compared to high salinity (33 PSU). Our study provides a base for future mechanistic studies on the role of aquaporins in osmoregulation.

The marine environment harbors a large proportion of the total biodiversity on this planet, including the majority of the earths' different phyla and classes. Studying the genomes of marine organisms can bring interesting insights into genome evolution. Today, almost all marine organismal groups are understudied with respect to their genomes. One potential reason is that extraction of high-quality DNA in sufficient amounts is challenging for many marine species. This is due to high polysaccharide content, polyphenols and other secondary metabolites that will inhibit downstream DNA library preparations. Consequently, protocols developed for vertebrates and plants do not always perform well for invertebrates and algae. In addition, many marine species have large population sizes and, as a consequence, highly variable genomes. Thus, to facilitate the sequence read assembly process during genome sequencing, it is desirable to obtain enough DNA from a single individual, which is a challenge in many species of invertebrates and algae. Here, we present DNA extraction protocols for seven marine species (four invertebrates, two algae, and a marine yeast), optimized to provide sufficient DNA quality and yield for de novo genome sequencing projects.

Shallow coastal waters are characterized by substantial diurnal fluctuations in pH, especially in nearshore environments. The biological effects of ocean acidification in combination with these natural fluctuations have received relatively little attention to date. We exposed multiple batches (≈ different genotypes) of newly settled barnacles, Balanus improvisus, to constant pH under “control” (pH = 8.1) or “stable acidified” (pH = 7.7) conditions, as well as a treatment that simulated the maximum diurnal pH fluctuations seen in the nearshore habitats where this barnacle lives (±0.2 pH units), superimposed on the stable acidified treatment (“fluctuating acidified”; 7.5 ≤ pH ≤ 7.9). We found that fluctuating acidification had no effect on mean response in growth and shell mineralogy, but caused an ∼20-fold increase in variance of responses, compared with stable acidification. In contrast to these results, we found no effect of fluctuating acidification on variances of response ratios for barnacle survival and shell strength. Similarly, mean survival did not vary significantly with pH. However, we observed a strong negative effect of stable and fluctuating acidification on mean shell strength. Our finding that barnacles respond differently to fluctuating pH than to stable low pH indicate the importance of including fluctuating acidification treatments when studying species that live in variable environments. Importantly, because phenotypic variance is the raw material for natural selection, and thus lays at the heart of evolutionary responses to environmental variability and change, our findings also highlight the need to study changes in variance of—as well as mean—responses to changing ocean climates.

BackgroundSalinity plays an important role in shaping coastal marine communities. Near-future climate predictions indicate that salinity will decrease in many shallow coastal areas due to increased precipitation; however, few studies have addressed this issue. The ability of ecosystems to cope with future changes will depend on species’ capacities to acclimatise or adapt to new environmental conditions. Here, we investigated the effects of a strong salinity gradient (the Baltic Sea system – Baltic, Kattegat, Skagerrak) on plasticity and adaptations in the euryhaline barnacle Balanus improvisus. We used a common-garden approach, where multiple batches of newly settled barnacles from each of three different geographical areas along the Skagerrak-Baltic salinity gradient were exposed to corresponding native salinities (6, 15 and 30 PSU), and phenotypic traits including mortality, growth, shell strength, condition index and reproductive maturity were recorded.ResultsWe found that B. improvisus was highly euryhaline, but had highest growth and reproductive maturity at intermediate salinities. We also found that low salinity had negative effects on other fitness-related traits including initial growth and shell strength, although mortality was also lowest in low salinity. Overall, differences between populations in most measured traits were weak, indicating little local adaptation to salinity. Nonetheless, we observed some population-specific responses – notably that populations from high salinity grew stronger shells in their native salinity compared to the other populations, possibly indicating adaptation to differences in local predation pressure.ConclusionsOur study shows that B. improvisus is an example of a true brackish-water species, and that plastic responses are more likely than evolutionary tracking in coping with future changes in coastal salinity.